U.S. patent number 10,133,416 [Application Number 15/199,395] was granted by the patent office on 2018-11-20 for signal detection in frequency division modulated touch systems.
This patent grant is currently assigned to Tactual Labs Co.. The grantee listed for this patent is Tactual Labs Co.. Invention is credited to Darren Laney Leigh.
United States Patent |
10,133,416 |
Leigh |
November 20, 2018 |
Signal detection in frequency division modulated touch systems
Abstract
A frequency division modulated touch detector having row and
column conductors arranged such that the path of the row conductors
cross the paths of the column conductors, and signal emitters
associated with each row, the emitters being adapted to transmit a
signal having a specific frequency and initial phase on each row
conductor, and a receiver associated with each column to receive
signals present on the column conductor. A signal processor is
adapted to determine an in-phase and a quadrature component for
each of the transmitted signal found in the received signals, and
to project a vector representing the transmitted frequencies at
their initial phase onto the respective in-phase and quadrature
component to determine a measurement for each transmitted signal on
each column, and create a heat map reflecting those measurements,
the heat map thus containing data reflective of touch.
Inventors: |
Leigh; Darren Laney (Round
Hill, VA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Tactual Labs Co. |
New York |
NY |
US |
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Assignee: |
Tactual Labs Co. (New York,
NY)
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Family
ID: |
58873874 |
Appl.
No.: |
15/199,395 |
Filed: |
June 30, 2016 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170329456 A1 |
Nov 16, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62336150 |
May 13, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06F
3/0418 (20130101); G06F 3/0412 (20130101); G06F
3/0416 (20130101); G06F 3/04166 (20190501); G06F
3/044 (20130101); G06F 2203/04108 (20130101); G06F
2203/04112 (20130101); G06F 2203/04105 (20130101) |
Current International
Class: |
G06F
3/041 (20060101); G06F 3/044 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ghebretinsae; Temesghen
Assistant Examiner: Cohen; Yaron
Attorney, Agent or Firm: Landa; Adam
Claims
What is claimed is:
1. A touch detector with an improved signal to noise ratio for
connection with a touch surface having a first set of conductors
and a second set of conductors, the touch detector comprising:
signal emitter adapted to transmit a unique one of a plurality of
original signals onto each of the first set of conductors, each of
the plurality of original signals having a respective initial phase
and a respective frequency, and each of the original signals being
frequency orthogonal to each of the other original signals;
receiver associated with each of the second set of conductors, to
receive signals present on the second set of conductors; and signal
processor being adapted to: (i) for each received signal, determine
an in-phase and a quadrature component for the respective
frequencies of each of the plurality of original signals, each pair
of in-phase and quadrature components defining a vector reflecting
a component of the received signal at the respective frequency; and
(ii) determine an estimate for each of the respective frequencies
by computing a dot product of a unit vector representing each
original signal at its corresponding respective phase and the
vector represented by the determined in-phase and quadrature
components; and (iii) identify touch on the touch surface based on
the estimates.
2. The touch detector according to claim 1, wherein the signal
processor and the receiver are part of the same component.
3. The touch detector according to claim 1, wherein the signal
processor and the receiver are not part of the same component.
4. The touch detector according to claim 1, wherein the respective
initial phase of one of the plurality of original signals is
different than the respective initial phase of another of the
plurality of original signals.
5. The touch detector according to claim 4, wherein the respective
initial phase of the one of the plurality of original signals is
the same as the respective initial phase of yet another of the
plurality of original signals.
6. The touch detector according to claim 1, wherein the respective
initial phase of one of the plurality of original signals is the
same as the respective initial phase of another of the plurality of
original signals.
7. A touch detector, comprising: first and second row conductors,
and a column conductor, arranged such that the capacitive effect of
bringing a finger into proximity causes a change in coupling
between the column conductor and at least one of the first and
second row conductors; first and second signal emitters
respectively adapted to transmit a first signal having a first
frequency at a first phase on the first row conductor and a second
signal having a second frequency at a second phase on the second
row conductor, each of the first and second signals being
orthogonal to the other; receiver associated with the column
conductor, to receive signals present on the column conductor;
signal processor being adapted to: determine an in-phase and a
quadrature component of the first and second frequencies in the
received signals; determine a first estimate for the first
frequency by computing a dot product of a first vector representing
the first frequency at its corresponding first phase and the vector
represented by the determined in-phase and quadrature components of
the first frequency; determine a second estimate for the second
frequency by computing a dot product of a second vector
representing the second frequency at its corresponding second phase
and the vector represented by the determined in-phase and
quadrature components of the second frequency; and detect touch
based on the first and second estimates.
8. The touch detector according to claim 7, wherein the signal
processor and the receiver are part of the same component.
9. The touch detector according to claim 7, wherein the signal
processor and the receiver are not part of the same component.
10. The touch detector according to claim 7, wherein at least one
of the first and second estimates is an estimate of power.
11. The touch detector according to claim 7, wherein at least one
of the first and second estimates is an estimate of amplitude.
12. The touch detector according to claim 7, wherein at least one
of the first and second estimates is proportional to an estimate of
amplitude.
13. The touch detector according to claim 7, wherein the signal
processor comprises more than one signal processor units, each of
the signal processor units adapted to perform at least one of the
following operations: determine an in-phase and a quadrature
component of the first and second frequencies in the received
signals; determine a first estimate for the first frequency by
computing a dot product of a first vector representing the first
frequency at its corresponding first phase and the vector
represented by the determined in-phase and quadrature components of
the first frequency; determine a second estimate for the second
frequency by computing a dot product of a second vector
representing the second frequency at its corresponding second phase
and the vector represented by the determined in-phase and
quadrature components of the second frequency; and detect touch
based on the first and second estimates; and all of the one or more
signal processor units, collectively, perform all of the
operations.
14. The touch detector according to claim 13, wherein at least one
of the first and second estimates is an estimate of power.
15. The touch detector according to claim 13, wherein at least one
of the first and second estimates is an estimate of amplitude.
16. The touch detector according to claim 13, wherein at least one
of the first and second estimates is proportional to an estimate of
amplitude.
17. A touch detector, comprising: a first row conductor and a first
column conductor arranged such that the path of the first row
conductor crosses the path of the first column conductor; signal
emitter adapted to transmit a first signal having a first frequency
at a first phase on the first row conductor; receiver associated
with the first column conductor, to receive signals present on the
first column conductor; signal processor being adapted to:
determine an in-phase and a quadrature component of the first
frequency in the signals received on the first column conductor,
the in-phase and quadrature components defining a vector reflecting
a component of the received signal at the first frequency; and
determine an estimate related to touch for the first frequency by
computing a dot product of a unit vector representing the first
frequency at the first phase and the vector represented by the
determined in-phase and quadrature components.
18. The touch detector according to claim 17, wherein the estimate
related to touch is an estimate of a power.
19. The touch detector according to claim 17, wherein the estimate
related to touch is an estimate of amplitude.
20. The touch detector according to claim 17, wherein the estimate
related to touch is proportional to an estimate of amplitude.
21. The touch detector according to claim 17, wherein the signal
processor comprises one or more signal processor units, each of the
one or more signal processor units is adapted to perform at least
one of the following operations: determine an in-phase and a
quadrature component of the first frequency in the received
signals; and determine an estimate related to touch for the first
frequency by computing a dot product of a unit vector representing
the first frequency at the first phase and the vector represented
by the determined in-phase and quadrature components; and all of
the one or more signal processor units, collectively, perform both
of the operations.
22. The touch detector according to claim 21, wherein the estimate
is an estimate of a power.
23. The touch detector according to claim 21, wherein the estimate
is an estimate of amplitude.
24. The touch detector according to claim 21, wherein the estimate
is proportional to an estimate of amplitude.
25. The touch detector according to claim 17, further comprising at
least one additional row conductor, the at least one additional row
conductor being arranged such that the path of the at least one
additional row conductor crosses the path of the first column
conductor.
26. The touch detector according to claim 25, wherein the at least
one additional row conductor is a plurality of additional row
conductors, and each of the plurality of additional row conductors
are arranged such that the path of each of the plurality of
additional row conductors crosses the path of the first column
conductor.
27. The touch detector according to claim 25, wherein there is at
least one additional column conductor arranged such that the path
of the at least one additional column conductor crosses the path of
the first row conductor and the path of the at least one additional
row conductor.
28. The touch detector according to claim 25, wherein the signal
emitter is further adapted to transmit at least one additional
signal having at least one additional frequency at et least one
additional phase on the at least one additional row conductor,
respectively, such that the signal emitter transmits a plurality of
unique orthogonal signals, each of the unique orthogonal signals
being orthogonal to each of the other unique orthogonal
signals.
29. The touch detector according to claim 17, further comprising at
least one additional column conductor, the one additional column
conductor being arranged such that the path of the at least one
additional column conductor crosses the path of the first row
conductor.
30. The touch detector according to claim 29, wherein: the receiver
is further associated with the at least one additional column
conductor, to receive signals present on the at least one
additional column conductor, and the signal processor is further
adapted to: determine an in-phase and a quadrature component of the
first frequency in the signals received on the at least one
additional column conductor; determine another estimate related to
touch for the first frequency by computing a dot product of a unit
vector representing the first frequency at the first phase and the
vector represented by the in-phase and quadrature components
determined for the signals received on the at least one additional
column conductor; and identify touch based on the estimate and the
another estimate.
31. The touch detector according to claim 30, wherein the another
amplitude estimate related to touch is an estimate of a power.
32. The touch detector according to claim 30, wherein the another
amplitude estimate related to touch is an estimate of
amplitude.
33. The touch detector according to claim 30, wherein the another
amplitude estimate related to touch is proportional to an estimate
of amplitude.
34. The touch detector according to claim 29, wherein the at least
one additional column conductor is a plurality of additional column
conductors, and each of the plurality of additional column
conductors are arranged such that the path of each of the plurality
of additional column conductors crosses the path of the first row
conductor.
35. The touch detector according to claim 29, further comprising at
least one additional row conductor arranged such that the path of
the at least one additional row conductor crosses the paths of the
first column conductor and the path of the at least one additional
column conductor.
36. The touch detector according to claim 35, wherein the signal
emitter is further adapted to transmit at least one additional
signal having at least one additional frequency at et least one
additional phase on the at least one additional row conductor,
respectively, such that the signal emitter transmits a plurality of
unique orthogonal signals, each of the unique orthogonal signals
being orthogonal to each of the other unique orthogonal
signals.
37. A method for detecting touch information on a touch detector,
the touch detector comprising first and second row conductors, at
least one column conductor, arranged such that the capacitive
effect of bringing a finger into proximity causes a change in
coupling between the column conductor and at least one of the first
and second row conductors, the touch detector further comprising a
receiver associated with at least one column conductor, and at
least one signal processor, the method comprising: transmitting a
first and second signal over the first and second row conductors,
respectively, the first signal being at a first frequency and a
first phase, and the second signal being at a second frequency and
a second phase, wherein the first and second frequencies are
orthogonal to each other; receiving signals present on the column
conductor; determining an in-phase and a quadrature component of
the first frequency in the received signal, the in-phase and
quadrature components of the first frequency defining a first
vector reflecting a component of the received signal at the first
frequency; determine a first estimate for the first frequency by
computing a dot product of a vector representing the first signal
at the first phase and the first vector; determining an in-phase
and a quadrature component of the second frequency in the received
signal, the in-phase and quadrature components of the second
frequency defining a second vector reflecting a component of the
received signal at the second frequency; determine a second
estimate for the second frequency by computing a dot product of a
second vector representing the second signal at the second phase
and the second vector; and creating a matrix reflecting the
detected estimates.
38. The method of claim 37, further comprising using the matrix to
determine touch.
39. The method of claim 37, further comprising: repeating the
transmitting step, the receiving step, the four determining steps
and the creating step, and using sequential matrices to detect
touch.
40. A method for detecting a touch event on a touch detector, the
touch detector comprising first and second row conductors, at least
one column conductor, arranged such that the capacitive effect of
bringing a finger into proximity causes a change in coupling
between the column conductor and at least one of the first and
second row conductors, the touch detector further comprising a
receiver associated with at least one column conductor, and at
least one signal processor, the method comprising: transmitting a
first and second signal over the first and second row conductors,
respectively, the first signal being at a first frequency and a
first phase, and the second signal being at a second frequency and
a second phase, wherein the first and second frequencies are
orthogonal to each other; receiving signals present on the column
conductor; and determining changes in an amount of each of the
first and the second signal present in the received signal;
identifying a touch event based upon the change in the amount of at
least one of the first and second signal present in the received
signals; wherein the step of determining changes in the amount of
each of the first and the second signal present in the received
signal comprises: determining an in-phase and a quadrature
component of the first frequency in the received signals at a first
time and determining a first estimate related to touch for the
first frequency by computing a dot product of a unit vector
representing the first frequency at the first phase and the vector
represented by the determined in-phase and quadrature components of
the first frequency in the received signal at the first time;
determining an in-phase and a quadrature component of the second
frequency in the received signals at the first time and determining
a first estimate related to touch for the second frequency by
computing a dot product of a unit vector representing the second
frequency at the second phase and the vector represented by the
determined in-phase and quadrature components of the second
frequency in the received signal at the first time; determining an
in-phase and a quadrature component of the first frequency in the
received signals at a second time and determining a second estimate
related to touch for the first frequency by computing a dot product
of a unit vector representing the first frequency at the first
phase and the vector represented by the determined in-phase and
quadrature components of the first frequency in the received signal
at the second time; determining an in-phase and a quadrature
component of the second frequency in the received signals at a
second time and determining a second estimate related to touch for
the second frequency by computing a dot product of a unit vector
representing the second frequency at the second phase and the
vector represented by the determined in-phase and quadrature
components of the second frequency in the received signal at the
second time; and comparing the first estimate related to touch for
the first frequency with the second estimate related to touch for
the first frequency, and comparing the first estimate related to
touch for the second frequency with the second estimate related to
touch for the second frequency, thereby determining changes in the
amount of each of the first and the second signal present in the
received signal.
41. The method of claim 40, wherein at least one of the first
estimate related to touch for the first frequency, the second
estimate related to touch for the first frequency, the first
estimate related to touch for the second frequency, and the second
estimate related to touch for the second frequency, is an estimate
of power.
42. The method of claim 40, wherein at least one of the first
estimate related to touch for the first frequency, the second
estimate related to touch for the first frequency, the first
estimate related to touch for the second frequency, and the second
estimate related to touch for the second frequency, is an estimate
of amplitude.
43. The method of claim 40, wherein at least one of the first
estimate related to touch for the first frequency, the second
estimate related to touch for the first frequency, the first
estimate related to touch for the second frequency, and the second
estimate related to touch for the second frequency, is proportional
to an estimate of amplitude.
44. A touch detector comprising: first and second row conductors,
and a column conductor, arranged such that the path of the first
and second row conductors cross the path of the column conductor;
first and second signal emitters each adapted to simultaneously
transmit one of a first and second signal on each of the first and
second row conductors, respectively; each of the two signals being
non-orthogonal to the other, the first signal differing from the
second signal in one selected from the group of: phase and
amplitude; receiver associated with the column conductor, to
receive signals present on the column conductor; signal processor
being adapted to: determine an in-phase and a quadrature component
of a combination of the first and second signals in the received
signals, the in-phase and quadrature components defining a combined
vector; determine a measurement related to touch for at least one
of the two signals by computing a dot product of a vector
representing one of the two signals at its phase and the combined
vector; and create a heat map reflecting touch using the
measurement.
45. The touch detector according to claim 44, wherein the first and
second signal emitters transmit other signals in conjunction with
the first and second signal on each of the first and second row
conductor.
46. The touch detector according to claim 44, wherein there is at
least one additional row, the at least one additional row conductor
arranged such that the path of the at least one additional row
conductor crosses the path of the column conductor.
47. The touch detector according to claim 44, wherein there is at
least one additional column conductor, the at least one additional
column conductor arranged such that it crosses the path of the
first and second row conductor.
Description
This application is a non-provisional of U.S. Provisional Patent
Application No. 62/336,150 filed May 13, 2016, the entire
disclosure of which is incorporated herein by reference.
FIELD
The disclosed system and method relate in general to the field of
user input, and in particular to improved signal detection in
frequency division modulated touch systems.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features, and advantages of the
disclosure will be apparent from the following more particular
description of embodiments as illustrated in the accompanying
drawings, in which reference characters refer to the same parts
throughout the various views. The drawings are not necessarily to
scale, emphasis instead being placed upon illustrating principles
of the disclosed embodiments.
FIG. 1 provides a high level block diagram illustrating an
embodiment of a low-latency touch sensor device.
FIG. 2 shows a block diagram illustrating a field flattening
procedure.
FIG. 3 shows the relationship between the in-phase and quadrature
representation and the amplitude and phase representation.
FIG. 4 shows the signal d corrupted by noise and interference
n.
FIG. 5 shows total noise is divided into components that are
parallel and perpendicular to the uncorrupted signal.
DETAILED DESCRIPTION
This application relates to user interfaces such as the fast
multi-touch sensors and other interfaces disclosed in U.S. patent
application Ser. No. 14/046,819 filed Oct. 4, 2013 entitled "Hybrid
Systems And Methods For Low-Latency User Input Processing And
Feedback," U.S. patent application Ser. No. 13/841,436 filed Mar.
15, 2013 entitled "Low-Latency Touch Sensitive Device," U.S. Patent
Application No. 61/798,948 filed Mar. 15, 2013 entitled "Fast
Multi-Touch Stylus," U.S. Patent Application No. 61/799,035 filed
Mar. 15, 2013 entitled "Fast Multi-Touch Sensor With
User-Identification Techniques," U.S. Patent Application No.
61/798,828 filed Mar. 15, 2013 entitled "Fast Multi-Touch Noise
Reduction," U.S. Patent Application No. 61/798,708 filed Mar. 15,
2013 entitled "Active Optical Stylus," U.S. Patent Application No.
61/710,256 filed Oct. 5, 2012 entitled "Hybrid Systems And Methods
For Low-Latency User Input Processing And Feedback," U.S. Patent
Application No. 61/845,892 filed Jul. 12, 2013 entitled "Fast
Multi-Touch Post Processing," U.S. Patent Application No.
61/845,879 filed Jul. 12, 2013 entitled "Reducing Control Response
Latency With Defined Cross-Control Behavior," U.S. Patent
Application No. 61/879,245 filed Sep. 18, 2013 entitled "Systems
And Methods For Providing Response To User Input Using Information
About State Changes And Predicting Future User Input," U.S. Patent
Application No. 61/880,887 filed Sep. 21, 2013 entitled "Systems
And Methods For Providing Response To User Input Using Information
About State Changes And Predicting Future User Input," U.S. patent
application Ser. No. 14/046,823 filed Oct. 4, 2013 entitled "Hybrid
Systems And Methods For Low-Latency User Input Processing And
Feedback," U.S. patent application Ser. No. 14/069,609 filed Nov.
1, 2013 entitled "Fast Multi-Touch Post Processing," and U.S.
Patent Application No. 61/887,615 filed Oct. 7, 2013 entitled
"Touch And Stylus Latency Testing Apparatus." The entire
disclosures of those applications are incorporated herein by
reference.
Throughout this disclosure, the terms "touch", "touches,"
"contact," "contacts" or other descriptors may be used to describe
events or periods of time in which a user's finger, a stylus, an
object or a body part is detected by the sensor. In some
embodiments, these detections occur only when the user is in
physical contact with a sensor, or a device in which it is
embodied. In other embodiments, the sensor may be tuned to allow
the detection of "touches" or "contacts" that are hovering a
distance above the touch surface or otherwise separated from the
touch sensitive device. Therefore, the use of language within this
description that implies reliance upon sensed physical contact
should not be taken to mean that the techniques described apply
only to those embodiments; indeed, nearly all, if not all, of what
is described herein would apply equally to "touch" and "hover"
sensors. More generally, as used herein, the term "touch" refers to
an act that can be detected by the types of sensors disclosed
herein, thus, as used herein the term "hover" is but one type of
"touch" in the sense that "touch" is intended herein. Other types
of sensors can be utilized in connection with the embodiments
disclosed herein, including a camera, a proximity sensor, an
optical sensor, a turn-rate sensor, a gyroscope, a magnetometer, a
thermal sensor, a pressure sensor, a force sensor, a capacitive
touch sensor, a power-management integrated circuit reading, a
keyboard, a mouse, a motion sensor, and the like.
The presently disclosed systems and methods provide systems and
methods for designing, manufacturing and using capacitive touch
sensors, and particularly capacitive touch sensors that employ a
multiplexing scheme based on orthogonal signaling such as but not
limited to frequency-division multiplexing (FDM), code-division
multiplexing (CDM), or a hybrid modulation technique that combines
both FDM and CDM methods. References to frequency herein could also
refer to other orthogonal signal bases. As such, this application
incorporates by reference Applicants' prior U.S. patent application
Ser. No. 13/841,436, filed on Mar. 15, 2013 entitled "Low-Latency
Touch Sensitive Device" and U.S. patent application Ser. No.
14/069,609 filed on Nov. 1, 2013 entitled "Fast Multi-Touch Post
Processing." These applications contemplate capacitive FDM, CDM, or
FDM/CDM hybrid touch sensors which may be used in connection with
the presently disclosed sensors. In such sensors, touches are
sensed when a signal from a row is coupled (increased) or decoupled
(decreased) to a column and the result received on that column.
This disclosure will first describe the operation of fast
multi-touch sensors to which the present systems and methods for
design, manufacturing and use can be applied. Details of the
presently disclosed frequency division modulated touch system and
method are then described further below under the heading "Signal
Detection."
As used herein, the phrase "touch event" and the word "touch" when
used as a noun include a near touch and a near touch event, or any
other gesture that can be identified using a sensor. In accordance
with an embodiment, touch events may be detected, processed and
supplied to downstream computational processes with very low
latency, e.g., on the order of ten milliseconds or less, or on the
order of less than one millisecond.
In an embodiment, the disclosed fast multi-touch sensor utilizes a
projected capacitive method that has been enhanced for high update
rate and low latency measurements of touch events. The technique
can use parallel hardware and higher frequency waveforms to gain
the above advantages. Also disclosed are methods to make sensitive
and robust measurements, which methods may be used on transparent
display surfaces and which may permit economical manufacturing of
products which employ the technique. In this regard, a "capacitive
object" as used herein could be a finger, other part of the human
body, a stylus, or any object to which the sensor is sensitive. The
sensors and methods disclosed herein need not rely on capacitance.
With respect to, e.g., the optical sensor, such embodiments utilize
photon tunneling and leaking to sense a touch event, and a
"capacitive object" as used herein includes any object, such as a
stylus or finger, that that is compatible with such sensing.
Similarly, "touch locations" and "touch sensitive device" as used
herein do not require actual touching contact between a capacitive
object and the disclosed sensor.
FIG. 1 illustrates certain principles of a fast multi-touch sensor
100 in accordance with an embodiment. At reference no. 200, a
different signal is transmitted into each of the surface's rows.
The signals are designed to be "orthogonal", i.e., separable and
distinguishable from each other. At reference no. 300, a receiver
is attached to each column. The receiver is designed to receive any
of the transmitted signals, or an arbitrary combination of them,
with or without other signals and/or noise, and to individually
determine a measure, e.g., a quantity for each of the orthogonal
transmitted signals present on that column. The touch surface 400
of the sensor comprises a series of rows and columns (not all
shown), along which the orthogonal signals can propagate. In an
embodiment, the rows and columns are designed so that, when they
are not subject to a touch event, a lower or negligible amount of
signal is coupled between them, whereas, when they are subject to a
touch event, a higher or non-negligible amount of signal is coupled
between them. In an embodiment, the opposite could hold--having the
lesser amount of signal represent a touch event, and the greater
amount of signal represent a lack of touch. Because the touch
sensor ultimately detects touch due to a change in the coupling, it
is not of specific importance, except for reasons that may
otherwise be apparent to a particular embodiment, whether the
touch-related coupling causes an increase in amount of row signal
present on the column or a decrease in the amount of row signal
present on the column. As discussed above, the touch, or touch
event does not require a physical touching, but rather an event
that affects the level of coupled signal.
With continued reference to FIG. 1, in an embodiment, generally,
the capacitive result of a touch event in the proximity of both a
row and column may cause a non-negligible change in the amount of
signal present on the row to be coupled to the column. More
generally, touch events cause, and thus correspond to, the received
signals on the columns. Because the signals on the rows are
orthogonal, multiple row signals can be coupled to a column and
distinguished by the receiver. Likewise, the signals on each row
can be coupled to multiple columns. For each column coupled to a
given row (and regardless of whether the coupling causes an
increase or decrease in the row signal to be present on the
column), the signals found on the column contain information that
will indicate which rows are being touched simultaneously with that
column. The quantity of each signal received is generally related
to the amount of coupling between the column and the row carrying
the corresponding signal, and thus, may indicate a distance of the
touching object to the surface, an area of the surface covered by
the touch and/or the pressure of the touch.
When a row and column are touched simultaneously, some of the
signal that is present on the row is coupled into the corresponding
column (the coupling may cause an increase or decrease of the row
signal on the column). (As discussed above, the term touch or
touched does not require actual physical contact, but rather,
relative proximity.) Indeed, in various implementations of a touch
device, physical contact with the rows and/or columns is unlikely
as there may be a protective barrier between the rows and/or
columns and the finger or other object of touch. Moreover,
generally, the rows and columns themselves are not in touch with
each other, but rather, placed in a proximity that allows an amount
of signal to be coupled there-between, and that amount changes
(positively or negatively) with touch. Generally, the row-column
coupling results not from actual contact between them, nor by
actual contact from the finger or other object of touch, but
rather, by the capacitive effect of bringing the finger (or other
object) into close proximity--which close proximity resulting in
capacitive effect is referred to herein as touch.
The nature of the rows and columns is arbitrary and the particular
orientation is irrelevant. Indeed, the terms row and column are not
intended to refer to a square grid, but rather to a set of
conductors upon which signal is transmitted (rows) and a set of
conductors onto which signal may be coupled (columns). (The notion
that signals are transmitted on rows and received on columns itself
is arbitrary, and signals could as easily be transmitted on
conductors arbitrarily named columns and received on conductors
arbitrarily named rows, or both could arbitrarily be named
something else.) Further, it is not necessary that the rows and
columns be in a grid. Other shapes are possible as long as a touch
event will touch part of a "row" and part of a "column", and cause
some form of coupling. For example, the "rows" could be in
concentric circles and the "columns" could be spokes radiating out
from the center. And neither the "rows" nor the "columns" need to
follow any geometric or spatial pattern, thus, for example, the
keys on keyboard could be arbitrarily connected to form rows and
columns (related or unrelated to their relative positions.)
Moreover, it is not necessary for there to be only two types signal
propagation channels: instead of rows and columns, in an
embodiment, channels "A", "B" and "C" may be provided, where
signals transmitted on "A" could be received on "B" and "C", or, in
an embodiment, signals transmitted on "A" and "B" could be received
on "C". It is also possible that the signal propagation channels
can alternate function, sometimes supporting transmission and
sometimes supporting receipt. It is also contemplated that the
signal propagation channels can simultaneously support transmitters
and receivers--provided that the signals transmitted are
orthogonal, and thus separable, from the signals received. Three or
more types of antenna conductors may be used rather than just
"rows" and "columns." Many alternative embodiments are possible and
will be apparent to a person of skill in the art after considering
this disclosure.
As noted above, in an embodiment the touch surface 400 comprised of
a series of rows and columns, along which signals can propagate. As
discussed above, the rows and columns are designed so that, when
they are not being touched, one amount of signal is coupled between
them, and when they are being touched, another amount of signal is
coupled between them. The change in signal coupled between them may
be generally proportional or inversely proportional (although not
necessarily linearly proportional) to the touch such that touch is
less of a yes-no question, and more of a gradation, permitting
distinction between more touch (i.e., closer or firmer) and less
touch (i.e., farther or softer)--and even no touch. Moreover, a
different signal is transmitted into each of the rows. In an
embodiment, each of these different signals are orthogonal (i.e.,
separable and distinguishable) from one another. When a row and
column are touched simultaneously, signal that is present on the
row is coupled (positively or negatively), causing more or less to
appear in the corresponding column. The quantity of the signal that
is coupled onto a column may be related to the proximity, pressure
or area of touch.
A receiver 300 is attached to each column. The receiver is designed
to receive the signals present on the columns, including of any of
the orthogonal signals, or an arbitrary combination of the
orthogonal signals, and any noise or other signals present.
Generally, the receiver is designed to receive a frame of signals
present on the columns, and to identify the columns providing
signal. In an embodiment, the receiver (or a signal processor
associated with the receiver data) may determine a measure
associated with the quantity of each of the orthogonal transmitted
signals present on that column during the time the frame of signals
was captured. In this manner, in addition to identifying the rows
in touch with each column, the receiver can provide additional
(e.g., qualitative) information concerning the touch. In general,
touch events may correspond (or inversely correspond) to received
signals on the columns. For each column, the different signals
received thereon indicate which of the corresponding rows is being
touched in proximity with that column. In an embodiment, the amount
of coupling between the corresponding row and column may indicate,
e.g., the area of the surface covered by the touch, the pressure of
the touch, etc. In an embodiment, a change in coupling over time
between the corresponding row and column indicates a change in
touch at the intersection of the two.
Simple Sinusoid Embodiment
In an embodiment, the orthogonal signals being transmitted onto the
rows may be unmodulated sinusoids, each having a different
frequency, the frequencies being chosen so that they can be
distinguished from each other in the receiver. In an embodiment,
frequencies are selected to provide sufficient spacing between them
such that they can be more easily distinguished from each other in
the receiver. In an embodiment, frequencies are selected such that
no simple harmonic relationships exist between the selected
frequencies. The lack of simple harmonic relationships may mitigate
non-linear artifacts that can cause one signal to mimic
another.
Generally, a "comb" of frequencies, where the spacing between
adjacent frequencies is constant, and the highest frequency is less
than twice the lowest, will meet these criteria if the spacing
between frequencies, .DELTA.f, is at least the reciprocal of the
measurement period .tau.. For example, if it is desired to measure
a combination of signals (from a column, for example) to determine
which row signals are present once per millisecond (.tau.), then
the frequency spacing (.DELTA.f) must be greater than one kilohertz
(i.e., .DELTA.f>1/.tau.). According to this calculation, in an
example case with only ten rows, one could use the following
frequencies: Row 1: 5.000 MHz Row 6: 5.005 MHz Row 2: 5.001 MHz Row
7: 5.006 MHz Row 3: 5.002 MHz Row 8: 5.007 MHz Row 4: 5.003 MHz Row
9: 5.008 MHz Row 5: 5.004 MHz Row 10: 5.009 MHz
It will be apparent to one of skill in the art that frequency
spacing may be substantially greater than this minimum to permit
robust design. As an example, a 20 cm by 20 cm touch surface with
0.5 cm row/column spacing would require forty rows and forty
columns and necessitate sinusoids at forty different frequencies.
While a once per millisecond analysis rate would require only 1 KHz
spacing, an arbitrarily larger spacing is utilized for a more
robust implementation. In an embodiment, the arbitrarily larger
spacing is subject to the constraint that the maximum frequency
should not be more than twice the lowest (i.e.,
f.sub.max<2(f.sub.min)). Thus, in an exemplary embodiment, a
frequency spacing of 100 kHz with the lowest frequency set at 5 MHz
may be used, yielding a frequency list of 5.0 MHz, 5.1 MHz, 5.2
MHz, etc. up to 8.9 MHz.
In an embodiment, each of the sinusoids on the list may be
generated by a signal generator and transmitted on a separate row
by a signal emitter or transmitter. In an embodiment, the sinusoids
may be pre-generated. To identify the rows and columns that are
being simultaneously touched, a receiver receives any signals
present on the columns and a signal processor analyzes the signal
to determine which, if any, frequencies on the list appear. In an
embodiment, the identification can be supported with a frequency
analysis technique (e.g., Fourier transform), or by using a filter
bank. In an embodiment, the receiver receives a frame of column
signals, which frame is processed through an FFT, and thus, a
measure is determined for each frequency. In an embodiment, the FFT
provides an in-phase and quadrature measure for each frequency, for
each frame.
In an embodiment, from each column's signal, the receiver/signal
processor can determine a value (and in an embodiment an in-phase
and quadrature value) for each frequency from the list of
frequencies found in the signal on that column. In an embodiment,
where the value corresponding to a frequency is greater or lower
than some threshold, or changes from a prior value, that
information is used to identify a touch event between the column
and the row corresponding to that frequency. In an embodiment,
signal strength information, which may correspond to various
physical phenomena including the distance of the touch from the
row/column intersection, the size of the touch object, the pressure
with which the object is pressing down, the fraction of row/column
intersection that is being touched, etc. may be used as an aid to
localize the area of the touch event. In an embodiment, the
determined values are not self-determinative of touch, but rather
are further processed along with other values to determine touch
events.
Once values for each of the orthogonal frequencies have been
determined for at least two frequencies (corresponding to rows) or
for at least two columns, a two-dimensional map can be created,
with the value being used as, or proportional/inversely proportion
to, a value of the map at that row/column intersection. In an
embodiment, the signals' strengths are calculated for each
frequency on each column. Once signal strengths are calculated a
two-dimensional map may be created. In an embodiment, the signal
strength is the value of the map at that row/column intersection.
In an embodiment, values are determined for multiple row/column
intersections on a touch surface to produce a map for the touch
surface or region. In an embodiment, values are determined for
every row/column intersection on a touch surface, or in a region of
a touch surface, to produce a map for the touch surface or region.
In an embodiment, due to physical differences in the touch surface
at different frequencies, the signal values are normalized for a
given touch or calibrated. Similarly, in an embodiment, due to
physical differences across the touch surface or between the
intersections, the signal values need to be normalized for a given
touch or calibrated.
In an embodiment, touch events are identified using a map produced
from the value information, and thus, take into account the value
changes of neighboring row/column intersections. In an embodiment,
the two-dimensional map data may be thresholded to better identify,
determine or isolate touch events. In an embodiment, the
two-dimensional map data may be used to infer information about the
shape, orientation, etc. of the object touching the surface.
In an embodiment, such analysis and touch processing described
herein may be performed on a touch sensor's discrete touch
controller. In another embodiment, such analysis and touch
processing may be performed on other computer system components
such as but not limited to one or more ASIC, MCU, FPGA, CPU, GPU,
SoC, DSP or dedicated circuit. The term "hardware processor" as
used herein means any of the above devices or any other device (now
known or hereinafter developed) which performs computational
functions.
Returning to the discussion of the signals being transmitted on the
rows, a sinusoid is not the only orthogonal signal that can be used
in the configuration described above. Indeed, as discussed above,
any set of signals that can be distinguished from each other will
work. Nonetheless, sinusoids may have some advantageous properties
that may permit simpler engineering and more cost efficient
manufacture of devices which use this technique. For example,
sinusoids have a very narrow frequency profile (by definition), and
need not extend down to low frequencies, near DC. Moreover,
sinusoids can be relatively unaffected by 1/f noise, which noise
could affect broader signals that extend to lower frequencies.
In an embodiment, sinusoids may be detected by a filter bank. In an
embodiment, sinusoids may be detected by frequency analysis
techniques (e.g., Fourier transform/fast Fourier transform).
Frequency analysis techniques may be implemented in a relatively
efficient manner and may tend to have good dynamic range
characteristics, allowing them to detect and distinguish between a
large number of simultaneous sinusoids. In broad signal processing
terms, the receiver's decoding of multiple sinusoids may be thought
of as a form of frequency-division multiplexing. In an embodiment,
other modulation techniques such as time-division and code-division
multiplexing can also be used. Time division multiplexing has good
dynamic range characteristics, but typically requires that a finite
time be expended transmitting into (or analyzing received signals
from) the touch surface. Code division multiplexing has the same
simultaneous nature as frequency-division multiplexing, but may
encounter dynamic range problems and may not distinguish as easily
between multiple simultaneous signals.
As disclosed in U.S. patent application Ser. No. 13/841,436,
entitled, "Low-Latency Touch Sensitive Device," a modulated
sinusoid may be used in lieu of, and as an enhancement of, the
simple sinusoid embodiment described above. The entire disclosure
of the application is incorporated herein by reference.
Touch surfaces using the previously described techniques may have a
relatively high cost associated with generating and detecting
sinusoids compared to other methods. Below are discussed methods of
generating and detecting sinusoids that may be more cost-effective
and/or be more suitable for mass production.
Sinusoid Detection
In an embodiment, sinusoids may be detected in a receiver using a
complete radio receiver with a Fourier Transform detection scheme.
Such detection may require digitizing a high-speed RF waveform and
performing digital signal processing thereupon. Separate
digitization and signal processing may be implemented for every
column of the surface; this permits the signal processor to
discover which of the row signals are in touch with that column. In
the above-noted example, having a touch surface with forty rows and
forty columns, would require forty copies of this signal chain.
Today, digitization and digital signal processing are relatively
expensive operations, in terms of hardware, cost, and power. It
would be useful to utilize a more cost-effective method of
detecting sinusoids, especially one that could be easily replicated
and requires very little power.
In an embodiment, sinusoids may be detected using a filter bank. A
filter bank comprises an array of bandpass filters that can take an
input signal and break it up into the frequency components
associated with each filter. The Discrete Fourier Transform (DFT,
of which the FFT is an efficient implementation) is a form of a
filter bank with evenly-spaced bandpass filters that may be used
for frequency analysis. DFTs may be implemented digitally, but the
digitization step may be expensive. It is possible to implement a
filter bank out of individual filters, such as passive LC (inductor
and capacitor) or RC active filters. Inductors are difficult to
implement well on VLSI processes, and discrete inductors are large
and expensive, so it may not be cost effective to use inductors in
the filter bank.
At lower frequencies (about 10 MHz and below), it is possible to
build banks of RC active filters on VLSI. Such active filters may
perform well, but may also take up a lot of die space and require
more power than is desirable.
At higher frequencies, it is possible to build filter banks with
surface acoustic wave (SAW) filter techniques. These allow nearly
arbitrary FIR filter geometries. SAW filter techniques require
piezoelectric materials which are more expensive than straight CMOS
VLSI. Moreover, SAW filter techniques may not allow enough
simultaneous taps to integrate sufficiently many filters into a
single package, thereby raising the manufacturing cost.
In an embodiment, sinusoids may be detected using an analog filter
bank implemented with switched capacitor techniques on standard
CMOS VLSI processes that employs an FFT-like "butterfly" topology.
The die area required for such an implementation is typically a
function of the square of the number of channels, meaning that a
64-channel filter bank using the same technology would require only
1/256th of the die area of the 1024-channel version. In an
embodiment, the complete receive system for the low-latency touch
sensor is implemented on a plurality of VLSI dies, including an
appropriate set of filter banks and the appropriate amplifiers,
switches, energy detectors, etc. In an embodiment, the complete
receive system for the low-latency touch sensor is implemented on a
single VLSI die, including an appropriate set of filter banks and
the appropriate amplifiers, switches, energy detectors, etc. In an
embodiment, the complete receive system for the low-latency touch
sensor is implemented on a single VLSI die containing n instances
of an n-channel filter bank, and leaving room for the appropriate
amplifiers, switches, energy detectors, etc.
Sinusoid Generation
Generating the transmit signals (e.g., sinusoids) in a low-latency
touch sensor is generally less complex than detection, principally
because each row requires the generation of a single signal (or a
small number of signals) while the column receivers have to detect
and distinguish between many signals. In an embodiment, sinusoids
can be generated with a series of phase-locked loops (PLLs), each
of which multiply a common reference frequency by a different
multiple.
In an embodiment, the low-latency touch sensor design does not
require that the transmitted sinusoids are of very high quality,
but rather, may accommodate transmitted sinusoids that have more
phase noise, frequency variation (over time, temperature, etc.),
harmonic distortion and other imperfections than may usually be
allowable or desirable in radio circuits. In an embodiment, the
large number of frequencies may be generated by digital means and
then employ a relatively coarse digital-to-analog conversion
process. As discussed above, in an embodiment, the generated row
frequencies should have no simple harmonic relationships with each
other, any non-linearities in the generation process should not
cause one signal in the set to "alias" or mimic another.
In an embodiment, a frequency comb may be generated by having a
train of narrow pulses filtered by a filter bank, each filter in
the bank outputting the signals for transmission on a row. The
frequency "comb" is produced by a filter bank that may be identical
to a filter bank that can be used by the receiver. As an example,
in an embodiment, a 10 nanosecond pulse repeated at a rate of 100
kHz is passed into the filter bank that is designed to separate a
comb of frequency components starting at 5 MHz, and separated by
100 kHz. The pulse train as defined would have frequency components
from 100 kHz through the tens of MHz, and thus, would have a signal
for every row in the transmitter. Thus, if the pulse train were
passed through an identical filter bank to the one described above
to detect sinusoids in the received column signals, then the filter
bank outputs will each contain a single sinusoid that can be
transmitted onto a row.
Transparent Display Surface
It may be desirable that the touch surface be integrated with a
computer display so that a person can interact with
computer-generated graphics and imagery. While front projection can
be used with opaque touch surfaces and rear projection can be used
with translucent ones, modern flat panel displays (LCD, plasma,
OLED, etc.) generally require that the touch surface be
transparent. In an embodiment, the present technique's rows and
columns, which allow signals to propagate along them, need to be
conductive to those signals. In an embodiment, the present
technique's rows and columns, which allow radio frequency signals
to propagate along them, need to be electrically conductive.
If the rows and columns are insufficiently conductive, the
resistance per unit length along the row/column will combine with
the capacitance per unit length to form a low-pass filter: any
high-frequency signals applied at one end will be substantially
attenuated as they propagate along the poor conductor.
Visually transparent conductors are commercially available (e.g.,
indium-tin-oxide or ITO), but the tradeoff between transparency and
conductivity is problematic at the frequencies that may be
desirable for some embodiments of the low-latency touch sensor
described herein: if the ITO were thick enough to support certain
desirable frequencies over certain lengths, it may be
insufficiently transparent for some applications. In an embodiment,
the rows and/or columns may be formed entirely, or at least
partially, from graphene and/or carbon nanotubes, which are both
highly conductive and optically transparent.
In an embodiment, the rows and/or columns may be formed from one or
more fine wires that block a negligible amount of the display
behind them. In an embodiment, the fine wires are too small to see,
or at least too small to present a visual impediment when viewing a
display behind it. In an embodiment, fine silver wires patterned
onto transparent glass or plastic can be used to make up the rows
and/or columns. Such fine wires need to have sufficient cross
section to create a good conductor along the row/column, but it is
desirable (for rear displays) that such wires are small enough and
diffuse enough to block as little of the underlying display as
appropriate for the application. In an embodiment, the fine wire
size is selected on the basis of the pixels size and/or pitch of
the underlying display.
As an example, the new Apple Retina displays comprises about 300
pixels per inch, which yields a pixel size of about 80 microns on a
side. In an embodiment, a 20 micron diameter silver wire 20
centimeters long (the length of an iPad display), which has a
resistance of about 10 ohms, is used as a row and/or column and/or
as part of a row and/or column in a low-latency touch sensor as
described herein. Such 20 micron diameter silver wire, however, if
stretched across a retina display, may block up to 25% of an entire
line of pixels. Accordingly, in an embodiment, multiple thinner
diameter silver wires may be employed as a column or row, which can
maintain an appropriate resistance, and provide acceptable response
with respect to radiofrequency skin depth issues. Such multiple
thinner diameter silver wires can be laid in a pattern that is not
straight, but rather, somewhat irregular. A random or irregular
pattern of thinner wires is likely to be less visually intrusive.
In an embodiment, a mesh of thin wires is used; the use of a mesh
will improve robustness, including against manufacturing flaws in
patterning. In an embodiment, single thinner diameter wires may be
employed as a column or row, provided that the thinner wire is
sufficiently conductive to maintain an appropriate level
resistance, and acceptable response with respect to radiofrequency
skin depth issues.
As used below, for convenience of description, the terms
transmitting conductor and receiving conductor will be used. The
transmitting conductor may be a row or column carrying a signal
e.g., from a signal generator. In this respect, "conductor" as used
herein includes not only electrical conductors but other paths on
which signals flow. A receiving conductor may be a row or column
carrying a signal resulting from the coupling of a touch event when
a touch event occurs in the proximity of the receiving conductor,
and not carrying the signal resulting from the coupling of a touch
event when no touch event occurs in the proximity of the receiving
conductor. In an embodiment, a receiver/signal processor measures
one or more quantities related to each of the orthogonal
transmitted signal on a receiving conductor which signals change
over time as a result of coupling (positive or negative) of a touch
event. The measuring of the one or more quantities allows for
identification of a touch event. In an embodiment, the
receiver/signal processor may comprise a DSP, a filter bank, or a
combination thereof. In an embodiment, the receiver/signal
processor is a comb filter providing bands corresponding to the
orthogonal signals.
Because any touch event in proximity to a row-column intersection
may change both the row-signal present on the column, and the
column-signal present on the row, in an embodiment, any signal on a
column or row that does not have a corresponding row or column
counterpart may be mitigated or rejected. In an embodiment, a
row-signal received at a column receiver/signal processor is used
in locating or identifying a touch event if a corresponding
column-signal is received at a corresponding row receiver/signal
processor. For example, a detected signal from Row R in Column C is
only considered to be caused by a touch event if Column C's
transmitted signal is also detected in Row R. In an embodiment,
Column C and Row R simultaneously transmit signals that are
orthogonal to the other row and column signals, and orthogonal to
each other. In an embodiment, Column C and Row R do not
simultaneously transmit signals, but rather, each transmits its
signal in an allotted time slice. In such an embodiment, signals
only require frequency- or code-orthogonality from other signals
transmitted in the same time slice.
As illustrated, in an embodiment, a single signal generator may be
used to generate the orthogonal signals for both the rows and the
columns, and a single signal processor may be used to process the
received signals from both the rows and the columns. In an
embodiment, one signal generator is dedicated to generating row
signals and a separate signal generator is dedicated to generating
column signals. In an embodiment, a plurality of signal generators
is dedicated to generating row signals and the same, or a separate
plurality of signal generators is dedicated to generating column
signals. Likewise, in an embodiment, one signal processor is
dedicated to processing row signals and a separate signal processor
is dedicated to processing column signals. In an embodiment, a
plurality of signal processors are dedicated to processing row
signals and the same, or a separate plurality of signal processors
are dedicated to processing column signals.
In an embodiment, each row and each column may be associated with a
signal, and the signal associated with each row or column is unique
and orthogonal with respect to the signal for every other row or
column. In such an embodiment, it may be possible to "transmit" all
row and column signals simultaneously. Where design or other
constraints require, or where it is desirable to use fewer than one
signal per row and column, time division multiplexing may be
employed.
As disclosed in U.S. patent application Ser. No. 14/603,104, filed
Jan. 22, 2015, entitled "Dynamic Assignment of Possible Channels in
a Touch Sensor," a system and method enables a touch sensor to
reduce or eliminate such false or noisy readings and maintain a
high signal-to-noise ratio, even if it is proximate to interfering
electromagnetic noise from other computer system components or
unwanted external signals. This method can also be used to
dynamically reconfigure the signal modulation scheme governing
select portions or the entire surface-area of a touch sensor at a
given point in time in order to lower the sensor's total power
consumption, while still optimizing the sensor's overall
performance in terms of parallelism, latency, sample-rate, dynamic
range, sensing granularity, etc. The entire disclosure of the
application is incorporated herein by reference.
Fast Multi-Touch Post Processing
After the signal strengths from each row in each column have been
calculated using, for example, the procedures described above,
post-processing is performed to convert the resulting 2-D "heat
map," also referred to as a "matrix," into usable touch events. In
an embodiment, such post processing includes at least some of the
following four procedures: field flattening, touch point detection,
interpolation and touch point matching between frames. The field
flattening procedure subtracts an offset level to remove crosstalk
between rows and columns, and compensates for differences in
amplitude between particular row/column combinations due to
attenuation. The touch point detection procedure computes the
coarse touch points by finding local maxima in the flattened
signal. The interpolation procedure computes the fine touch points
by fitting data associated with the coarse touch points to a
paraboloid. The frame matching procedure matches the calculated
touch points to each other across frames. Below, each of the four
procedures is described in turn. Also disclosed are examples of
implementation, possible failure modes, and consequences, for each
processing step. Because of the requirement for very low latency,
the processing steps should be optimized and parallelized.
A field flattening procedure may be used to reduce systematic
issues that cause artifacts in each column's received signal
strength. In an embodiment, these artifacts may be compensated-for
as follows. First, because of cross-talk between the rows and
columns, the received signal strength for each row/column
combination will experience an offset level. To a good
approximation, this offset level will be constant and can be
subtracted (or added) off
Second, the amplitude of the signal received at a column due to a
calibrated touch at a given row and column intersection will depend
on that particular row and column, mostly due to attenuation of the
signals as they propagate along the row and column. The farther
they travel, the more attenuation there will be, so columns farther
from the transmitters and rows farther from the receivers will have
lower signal strengths in the "heat map" than their counterparts.
If the RF attenuation of the rows and columns is low, the signal
strength differences may be negligible and little or no
compensation will be necessary. If the attenuation is high,
compensation may be necessary or may improve the sensitivity or
quality of touch detection. Generally, the signal strengths
measured at the receivers are expected to be linear with the amount
of signal transmitted into the columns. Thus, in an embodiment,
compensation will involve multiplying each location in the heat map
by a calibration constant for that particular row/column
combination. In an embodiment, measurements or estimates may be
used to determine a heat map compensation table, which table can be
similarly used to provide the compensation by multiplication. In an
embodiment, a calibration operation is used to create a heat map
compensation table. The term "heat map" as used herein does not
require an actual map of heat, but rather the term can mean any
array of at least two dimensions comprising data corresponding to
locations.
In an exemplary embodiment, the entire field flattening procedure
is as follows. With nothing touching the surface, first the signal
strength for each row signal at each column receiver is measured.
Because there are no touches, substantially the entire signal
received is due to cross-talk. The value measured (e.g., the amount
of each row's signal found on each column) is an offset level that
needs to be subtracted from that position in the heat map. Then,
with the constant offsets subtracted, a calibrated touch object is
placed at row/column intersections and the signal strength of that
row's signal at that column receiver is measured. In an embodiment,
all row/column intersections are used for calibration. The signal
processor may be configured to normalize the touch events to the
value of one location on the touch surface. The location likely to
have the strongest signals can be arbitrarily chosen (because it
experiences the least attenuation), i.e., the row/column
intersection closest to the transmitters and receivers. If the
calibrated touch signal strength at this location is S.sub.N and
the calibrated touch signal strength for each row and column is
S.sub.R,C then, if each location in the heat map is multiplied by
(S.sub.N/S.sub.R,C), all touch values will be normalized. In an
embodiment, calibrated touches may cause the normalized signal
strength for any row/column in the heat map to be equal to one.
The field flattening procedure parallelizes well. Once the offsets
and normalization parameters are measured and stored--which should
only need to be done once (or possibly again at a maintenance
interval)--the corrections can be applied as soon as each signal
strength is measured. FIG. 2 illustrates an embodiment of a field
flattening procedure.
In an embodiment, calibrating each row/column intersection may be
required at regular or selected maintenance intervals. In an
embodiment, calibrating each row/column intersection may be
required once per unit. In an embodiment, calibrating each
row/column intersection may be required once per design. In an
embodiment, and particularly where, e.g., RF attenuation of the
rows and columns is low, calibrating each row/column intersection
may not be required at all. Moreover, in an embodiment where the
signal attenuation along the rows and columns is fairly
predictable, it may be possible to calibrate an entire surface from
only a few intersection measurements.
If a touch surface does experience a lot of attenuation, the field
flattening procedure will, at least to some degree, normalize the
measurements, but it may have some side effects. For example, the
noise on each measurement will grow as its normalization constant
gets larger. It will be apparent to one of skill in the art, that
for lower signal strengths and higher attenuations, this may cause
errors and instability in the touch point detection and
interpolation processes. Accordingly, in an embodiment sufficient
signal strength is provided for the signal undergoing the largest
attenuation (e.g., the farthest row/column intersection). In an
embodiment, after the heat map is generated and the field
flattened, touch points can be identified.
Use Duplication of Sensing to Increase the Sensor's Signal-to-Noise
Ratio
A touch sensor can also utilize a number of techniques to decrease
the influence of interference and other noise in the touch sensor.
For example, in an embodiment for a touch sensor that employs FDM,
a touch sensor could use multiple frequencies per row so that, even
if the sensor cannot predict which frequency bins will be subject
to interference, then it can measure each row (or column) in
multiple ways and gauge the least noisy measurement (or combination
of measurements), and then use those.
In cases where it is difficult to decide whether a measurement has
been affected by interference or not, a touch sensor could employ a
voting scheme whereby a voting plurality of measurements, or a
similar statistical method, is used to determine which measurements
to throw away, which to keep and the best way to statistically and
mathematically combine the ones it keeps to maximize the
signal-to-noise+interference ratio and thereby enhance the user
experience. For example, in an embodiment, an FDM touch sensor
subject to interference could transmit three different frequencies
on each row, (where the frequencies are sufficiently separated so
that interference between them is statistically unlikely) and
measure the results. Then using a two-out-of-three voting system,
the sensor can determine which of the frequencies has been degraded
the most by interference and, either remove its measurement from
consideration in the final measurement, or combine the remaining
two in a statistically plausible manner (given what the sensor
"knows" a priori about the interference and noise statistics) or
include all three and combine them in a statistically plausible
manner, weighting the influence of each frequency measurement by
the statistical likelihood of its degradation by noise and
interference.
Some methods that a touch sensor can employ in this manner include
but are not limited to: 1. Using multiple frequencies per row.
These frequencies could be employed simultaneously or in sequence.
2. Transmitting from rows to columns, and from columns to rows,
which can also be combined with the use of multiple frequencies
above or with another combination of modulation schemes. 3. Using
CDMA on top of FDM, or some combination of modulation schemes. Here
it should be noted that CDMA signals, unlike those commonly
employed by FDM techniques, are fundamentally "unnatural" and
therefore are often more immune than FDM modulation schemes to a
variety of naturally-occurring signals in a computer system's
external environment. Improved Signal Detection
The presently disclosed frequency division modulated touch system
is used for connection with a touch surface. A frequency division
modulated touch system must determine the power (or amplitude) of
received signals in order to determine whether a touch event has
occurred. Power and amplitude have a functional or proportional
relationship, meaning that when one changes the other changes in a
predictable manner. Power is normally calculated by taking the
sum-of-squares of the real and imaginary components of an FFT at
the frequency of interest. The sum-of-squares operations require
two scalar multiplications and an addition to determine the power
of the estimated signal, as well as a subsequent square root
operation to determine the amplitude.
It has been discovered that where the phase of the signal of
interest is known, its amplitude can be estimated with higher
signal-to-noise ratio (SNR) by projecting the complex FFT output at
that frequency along the unit vector that has the known phase of
the received signal. This discovery excludes noise that would
normally be included in the sum-of-squares calculation, thereby
increasing the SNR of amplitude estimation. In an embodiment, half
of the noise included in the sum-of-squares calculation is
excluded, resulting in an SNR improvement of 3 dB. Moreover, the
novel method of amplitude estimation may be implemented using two
scalar multiplications and an addition to determine the amplitude
of the estimated signal. Thus, using the novel approach disclosed
herein, both the SNR and the computational efficiency may be
improved.
The measurement of a particular signal at some frequency has two
degrees of freedom; it is therefore a vector of length two. This
can be expressed in polar coordinates as amplitude and phase (i.e.,
the magnitude and angle of the polar vector), but it can also be
expressed in Cartesian coordinates, and usually is designated
"in-phase" and "quadrature". See FIG. 3, which shows the
relationship between the in-phase and quadrature representation and
the amplitude and phase representation.
One of skill in the art will understand that the phase of a
sinusoid is arbitrary because it depends on a particular reference
point and time. Considering a chosen reference point, a cosine
signal will be maximum at that point at time t=0, and will then
decrease in amplitude. A sine signal will be zero at that point at
time t=0 and will then increase in amplitude. A cosine signal is
completely in-phase, meaning that its vector lies along the x-axis.
A sine signal is completely quadrature, meaning that its vector
lies along the y-axis. A signal with some other phase will have
both in-phase and quadrature components, and its vector will lie
between the axes.
Conversion between polar (r, .phi.) and cartesian (x, y)
coordinates can be done as follows: x=r cos(.phi.) r=hypot(x, y)=
{square root over (x.sup.2+y.sup.2)} y=r sin(.phi.) .PHI.=a tan
2(y, x)
If the phase of a signal measurement is known, one of skill in the
art can convert it to a different phase by rotating the vector to
the desired phase. In polar coordinates this is trivial, because
the phase difference can be added to the original phase. In
Cartesian coordinates, a rotation matrix can be used to rotate the
vector by the appropriate phase difference.
.function..DELTA..times..times..PHI..function..DELTA..times..times..PHI..-
function..DELTA..times..times..PHI..function..DELTA..times..times..PHI..fu-
nction. ##EQU00001## Where .DELTA..PHI. is the phase difference by
which the vector is rotated.
The output of a discrete Fourier transform, such as the FFT, is
complex. Complex numbers are used as a mathematical convenience to
express two-dimensional vectors. The real component represents the
x or in-phase component of the vectors, and the imaginary component
represents the y or quadrature component. Complex numbers can be
used in exponential form, through Euler's formula:
e.sup.iu=cos(u)+i sin(u) An amplitude term r along with the phase
term u can be included, which is sometimes referred to as a phasor:
re.sup.iu=r cos(u)+i r sin(u) The exponential form provides a
method to multiply two of the vectors in a useful way.
re.sup.iuse.sup.iv=rs e.sup.i(u+v) This formula represents that the
product of two vectors (or phasors) with amplitudes r and s,
respectively, and phase angles u and v, respectively, is a vector
with amplitude rs and a phase angle of u+v.
Discrete Fourier transforms have a certain relationship between
patterns in their input and patterns in their output. Specifically,
with A(f)=DFT(a(t)):
TABLE-US-00001 If the input is . . . Then the output is . . . Real,
i.e., imag(a(t)) = 0 Even/symmetric, i.e., A(f) = A(-f) Imaginary,
i.e., real(a(t)) = 0 Odd/anti-symmetric, i.e., A(f) = -A(-f)
Complex Neither even nor odd Even/symmetric, i.e., a(t) = a(-t)
Real, i.e., imag(A(f)) = 0 Odd/anti-symmetric, i.e., Imaginary,
i.e., real(A(f)) = 0 a(t) = -a(-t) Neither even nor odd Complex
In FDM-based touch systems, such as those taught in U.S. patent
application Ser. No. 15/099,179 filed 14 Apr. 2016 (the entire
disclosure of which is incorporated herein by reference), the time
domain data a(t) applied to the input of an FFT is real, but there
is no constraint on it being even or odd. When the duplicated part
is ignored, the outputs in the frequency domain are even and
complex. The output frequency bin A(f) contains a real component
(which is the in-phase or x component) and an imaginary component
(which is the quadrature or y component). The total power in that
bin can be computed by using the following: power in
A(f)=real(A(f)).sup.2+imag(A(f)).sup.2 The phase, referenced to
input bin a(t=0) of the FFT, is phase of A(f)=a tan2(imag(A(f)),
real(A(f)))
Because the touch systems described herein directly supply the
transmitted signal, and because the transmitters and receivers are
running in lock-step from the same clock, the phase of each row
signal should always be constant as seen in each column receiver.
Note that a touch on the touch sensor does effect the coupling
between row and column and may have an effect on the phase. This
effect is addressed later in a subsequent section herein.
The Effects of Noise
The receivers are associated with the columns, to receive column
signals present on the columns. Further, the receivers on the touch
systems described herein receive not only the deliberately
transmitted row signals, but also noise and interference. The noise
and interference is additive and is independent of the row signals
and independent in each channel. It can be modeled as follows:
{right arrow over (c)}={right arrow over (a)}+{right arrow over
(n)}
Where {right arrow over (c)}, the corrupted signal, is the sum of
{right arrow over (a)}, the deliberately generated row signal, and
{right arrow over (n)}, the noise and interference. FIG. 4 shows a
snapshot of the signal, {right arrow over (a)}, corrupted by noise
and interference {right arrow over (n)}.
The noise will corrupt the signal in two different ways. First, the
component of {right arrow over (n)} that is parallel to {right
arrow over (a)} causes amplitude noise, i.e., changes in the
amplitude of the sinusoidal signal. Second, the component of {right
arrow over (n)} that is perpendicular to {right arrow over (a)}
causes phase noise, i.e., changes in the phase of the sinusoidal
signal. Note that, on average, half of the noise energy goes into
amplitude noise and the other half goes into phase noise.
The above is strictly true only in the case of high signal-to-noise
ratio. While the parallel component of {right arrow over (n)}
always translates into amplitude noise, the perpendicular adds
mostly phase noise, but can also add some amplitude noise.
This is readily understood from FIG. 5. In FIG. 5, the total noise
is separated into components that are parallel and perpendicular to
the uncorrupted signal. The parallel component adds an error term
to the amplitude of the original signal, and so causes "amplitude
noise." The perpendicular component adds an error term to the phase
of the original signal, and so causes "phase noise." Note that the
perpendicular component does not exactly follow the radius of
constant amplitude, along which the original signal would rotate if
its phase changed. Meaning that, unless the perpendicular component
is small compared to the amplitude of the original signal, it will
contribute amplitude noise as well.
If the perpendicular component is small compared to the amplitude
of the uncorrupted signal, it will follow the radius of constant
amplitude, meaning that it will add phase noise but not amplitude
noise. However, if it gets large enough to deviate substantially
from the radius of constant curvature, then it will also contribute
amplitude noise along with phase noise.
Implications for FDM Touch Systems
Touch systems that use frequency division multiplexing (FDM), such
as FMT, are prone to additive noise and interference as described
above. The signal processing chain normally computes an FFT that
provides a complex output at each frequency of interest, and the
power can be calculated by taking the sum of the squares of the
real and imaginary components. To produce the amplitude, one would
have to take the square root of the power, which is computationally
expensive. Calculating the power or amplitude throws away all of
the phase information. The sum-of-squares calculation is:
.fwdarw..fwdarw..fwdarw..fwdarw..fwdarw..fwdarw..fwdarw..fwdarw..times..f-
wdarw..fwdarw..fwdarw..fwdarw..times..fwdarw..fwdarw..times..times..times.-
.times..times..phi. ##EQU00002## The magnitude of the
sum-of-squares calculation is its square root: c= {square root over
(a.sup.2+2an cos .phi.+n.sup.2)} Where .phi. is the phase angle of
the instantaneous noise vector, relative to the phase angle of the
uncorrupted signal.
The known-phase calculation is: d=a({right arrow over (a)}+{right
arrow over (n)})=a+n cos .phi. Where a is the unit vector in the
direction of {right arrow over (a)}. The power of the known-phase
calculation is its square: d.sup.2=(a+n cos
.phi.).sup.2=a.sup.2+2an cos .phi.+n.sup.2 cos .phi.
The power calculations can be directly compared by noting that
n.sup.2=n.sup.2 cos.sup.2 .phi.+n.sup.2 sin.sup.2 .phi. Thus
c.sup.2=a.sup.2+2an cos .phi.+n.sup.2=a.sup.2+2an cos .phi.+n.sup.2
cos.sup.2 .phi.+n.sup.2 sin.sup.2 .phi.
TABLE-US-00002 Power Calculations Equations Sum-of-Squares c.sup.2
= a.sup.2 + 2an cos .phi. + n.sup.2cos.sup.2.phi. +
n.sup.2sin.sup.2.phi. Known-Phase d.sup.2 = a.sup.2 + 2an cos .phi.
+ n.sup.2cos.sup.2.phi.
The difference between the two power methods is n.sup.2 sin.sup.2
.phi., which is always non-negative. Therefore, the power
calculated by the known-phase method will always be smaller than
that calculated by the sum-of-squares method. Because the
difference term contains only noise variables n and .phi., and not
the signal variable a, the difference is only composed of noise and
its elimination makes the measurement closer to the true value of
a.sup.2.
The magnitude calculations can be similarly compared, but the
result is less obvious because of the square root.
TABLE-US-00003 Magnitude Calculations Equations Sum-of- c = {square
root over (a.sup.2 + 2an cos .phi. n.sup.2)} Squares Known-Phase d
= a + n cos .phi.
In certain regimes, by introducing a signal-to-noise ratio variable
.gamma., which is equal to
##EQU00003## the reciprocal of me signal-noise-ratio or 1/SNR, each
of the equations becomes:
.times..times..times..times..times..phi..function..times..times..times..t-
imes..phi..function..times..times..gamma..times..times..times..times..phi.-
.gamma. ##EQU00004##
.times..times..times..times..times..phi..times..times..PHI..function..tim-
es..times..times..times..phi..times..times..phi..function..times..times..g-
amma..times..times..times..times..phi..gamma..times..times..phi.
##EQU00004.2##
.times..times..times..times..times..times..times..phi..times..times..time-
s..gamma..times..times..times..times..phi..gamma. ##EQU00004.3##
.times..times..times..times..times..phi..function..times..times..times..p-
hi..function..times..gamma..times..times..times..times..phi.
##EQU00004.4##
The various regimes can be compared. The first of these is the time
average, which can be determined by setting all of the sine and
cosine terms to zero (but not their powers since they have to first
be reduced to a non power form).
TABLE-US-00004 Calculation Complete Time Average SoS Power c.sup.2
= a.sup.2(1 + 2.gamma.cos .phi. + .gamma..sup.2) c.sup.2 =
a.sup.2(1 + .gamma..sup.2) = a.sup.2 + n.sup.2 KP Power d.sup.2 =
a.sup.2(1 + 2.gamma.cos .phi. + .gamma..sup.2cos.sup.2 .phi.)
.function..times..gamma..times. ##EQU00005## Sos Mag c = a{square
root over (1 + 2.gamma.cos .phi. + .gamma..sup.2)} c = a{square
root over (1 + .gamma..sup.2)} = {square root over (a.sup.2 +
n.sup.2)} KP Mag d = a(1 + .gamma.cos .phi.) d = a
The time average is the baseline of the measured signal, ignoring
deviations from it. The power of the known-phase measurement has
only half the noise contribution of the sum-of-squares measurement,
and thus has a 3 dB SNR improvement. The time average of the
sum-of-squares magnitude has a bias term and will always be larger
than the time average of the known-phase measurement.
Note that the known-phase calculation ignores the noise component
that is orthogonal to the known signal, i.e., the n sin .PHI.
component of {right arrow over (n)}. That component contains only
noise and none of the original signal, so there is zero utility in
including it.
In an embodiment, further note that the 3 dB reduction in noise is
an average, having been integrated over a large number of samples.
An estimate of the original signal amplitude calculated with the
known-phase technique may have just as much noise as an estimate
that uses the sum-of-squares technique (if the noise vector happens
to be parallel to the original signal vector), or no noise at all
(if the noise vector happens to be perpendicular to the original
signal vector). As long as the original signal phase is truly
known, the known-phase technique will never produce a result with
lower SNR than the sum-of-squares technique.
To determine the deviations from the time-averaged baseline,
instantaneous calculations must be used and the sine and cosine
terms cannot be omitted. Instead, the calculations in both the
high- and low-SNR regimes are used to see how each is affected.
Below is an examination of the high-SNR regime, in which n<<a
and therefore .gamma.<<1.
TABLE-US-00005 Calculation Complete High SNR SoS Power c.sup.2 =
a.sup.2(1 + 2.gamma.cos .phi. + .gamma..sup.2) c.sup.2 .apprxeq.
a.sup.2(1 + 2.gamma.cos .phi.) KP Power d.sup.2 = a.sup.2(1 +
2.gamma.cos .phi. + .gamma..sup.2cos.sup.2.phi.) d.sup.2 .apprxeq.
a.sup.2(1 + 2.gamma.cos .phi.) SoS Mag c = a{square root over (1 +
2.gamma.cos .phi. + .gamma..sup.2)} c .apprxeq. a{square root over
(1 + 2.gamma.cos .phi.)} .apprxeq. a (1 + .gamma.cos .phi.) KP Mag
d = a (1 + .gamma.cos .phi.) d .apprxeq. a (1 + .gamma.cos
.phi.)
Because .gamma.<<1, .gamma..sup.2<<.gamma. all
.gamma..sup.2 terms can be omitted if there are also .gamma. terms.
After such omissions, however, there is no advantage of using the
known-phase technique over the sum-of-squares technique, and vice
versa. In the high-SNR regime, all of these techniques perform
equally.
Below is an examination of the low-SNR regime, in which a<<n
and therefore .gamma.>>1 and
.gamma..sup.2>>.gamma..
TABLE-US-00006 Calculation Complete High SNR SoS Power c.sup.2 =
a.sup.2(1 + 2.gamma.cos .phi. + .gamma..sup.2) c.sup.2 .apprxeq.
n.sup.2 KP Power d.sup.2 = a.sup.2(1 + 2.gamma.cos .phi. +
.gamma..sup.2cos.sup.2 .phi.)
.apprxeq..times..function..times..times..times..phi. ##EQU00006##
Sos Mag c = a{square root over (1 + 2.gamma.cos .phi. +
.gamma..sup.2)} c .apprxeq. n KP Mag d = a(1 + .gamma.cos .phi.) d
.apprxeq. n cos .phi.
In the low-SNR regime, the signal a goes away and leaves only
noise. The known-phase technique never produces more noise than the
sum-of-squares technique, even on an instantaneous basis, and on
average produces only half of the noise. On an instantaneous basis,
the known-phase technique will sometimes produce the same amount of
noise as the sum-of-squares technique, and sometimes will produce
none.
In a real-world application, the SNR will be somewhere between the
two extremes.
Exemplary Embodiment
To estimate the original signal power using a sum-of-squares
technique, the complex value of the particular FFT output bin and
A(f) are used to calculate: power
estimate=P.sub.SoS(f)=real(A(f)).sup.2+imag(A(f)).sup.2 The
estimated amplitude is the square root of the power estimate. In an
embodiment, to estimate the original signal amplitude using the
known-phase technique, the known phase is required. In another
embodiment, this information can be obtained from design
information, or can be measured directly from the touch system. In
the presence of noise and interference, it would be best to average
or otherwise statistically combine many values of the particular
FFT output. In an embodiment, this may be done by averaging the
real and imaginary components separately, so the known phase would
therefore be: average known phase=.phi..sub.k=a tan
2(mean(imag(A(f))), mean(real(A(f)))) Then the known phase is
converted to a unit vector with that phase: u.sub.k=[cos
.phi..sub.k, sin .phi..sub.k] Taking the dot product of this unit
vector with the incoming complex samples will yield the amplitude
estimates at that frequency: amplitude estimate
Y.sub.KP(f)=real(A(f))cos .PHI..sub.k+imag(A(f))sin .PHI..sub.k The
corresponding power estimate P.sub.KP(f)=(Y.sub.KP(f)).sup.2. Note,
as would be understood by one of skill in the art, the dot product
operation above is half of the calculation for multiplication by a
rotation matrix. It will also be apparent to one of skill in the
art in view of this disclosure that other statistical combinations
may be useful instead of average, such as, e.g., median, or mode,
or other measure that reflects a characteristic of the values.
It should be noted that no trigonometric functions are required in
the embedded system itself. These can be computed beforehand,
either at design time or at calibration time, if they are needed at
all. In fact, no trigonometric functions may be needed at all. The
unit vector u.sub.k=[cos .phi..sub.k, sin .phi..sub.k] is just the
average of the real and imaginary values, which has then been
normalized. If it is necessary for the unit vectors to be computed
by the embedded device itself (during a power-on calibration
interval, perhaps), the most expensive computation needed is a
division operator for the normalization. The division operator must
be done once for each row frequency and then is never used
again.
Non-constant Signal Phase
Where the transmitted phase is not constant relative to the
receiver, a touch on the sensor causes a phase change between the
transmitter and receiver, or the phase was measured incorrectly,
then that could result in the phase of the original signal not
being constant or otherwise not matching the "known" phase used in
the calculation.
Small phase differences make little difference in the final
signal-to-noise ratio, however. The phase error would affect only
the original signal, but not the noise (on average) because the
angle between the noise and the signal is uncorrelated.
In an embodiment, using the known-phase technique, a phase
difference of .DELTA..PHI. would lower the amplitude of the
received signal by cos .DELTA..PHI., and therefore its power by
cos.sup.2 .DELTA..PHI.. In another embodiment, a phase difference
of 10 degrees would lower the measured SNR by 0.13 dB. In another
embodiment, a difference of 30 degrees would lower the SNR by 1.25
dB and a difference of 45 degrees would lower the SNR by 3 dB. On
average, use of the known-phase technique will have an SNR
advantage as long as the average phase error does not exceed 45
degrees.
In an embodiment, use of the known-phase technique to compute the
estimated amplitude of a transmitted signal will provide an average
SNR improvement of 3 dB, while requiring approximately the same
amount of computational resources as the existing sum-of-squares
technique. Even fewer resources are required if amplitude results
are preferred over power results because the amplitude is
calculated directly with no need to compute a square root.
In an embodiment, the only additional resources required are the
measurement of the known signal phases, which can be calculated at
design time or measured after a device is built, and two memory
storage location per used FFT frequency bin. Each storage location
must be able to hold a scalar with value between -1 and +1.
Any of the resulting measurements can be a measurement of power, a
measurement of amplitude, or is proportional to a measurement of
amplitude.
In an embodiment, the touch detector is comprised of one or more
rows and one or more columns of conductive material, at least one
signal emitter, at least one receiver, and at least one signal
processor.
In some exemplary embodiments, the rows and columns are arranged in
a matrix of rows and columns of conductive material. In another
embodiment, the touch detector contains first and second row
conductors, and a column conductor, arranged such that the path of
the first and second row conductors cross the path of the column
conductor. In another embodiment, the touch detector contains at
least one first row conductor and at least one first column
conductor arranged such that the path of the first row conductor
crosses the path of the first column conductor.
In another embodiment, a first row conductor and a first column
conductor arranged such that the path of the first row conductor
crosses the path of the first column conductor. Additionally, at
least one additional row conductor is present, and is arranged such
that the path of the at least one additional row conductor crosses
the path of the first column conductor. Additionally, the at least
one additional row conductor is a plurality of additional row
conductors, and each of the plurality of additional row conductors
are arranged such that the path of each of the plurality of
additional row conductors crosses the path of the first column
conductor. In another embodiment, there is at least one additional
column conductor arranged such that the path of the at least one
additional column conductor crosses the path of the first row
conductor and the path of the at least one additional row
conductor. In an embodiment, there is at least one additional
column conductor, the one additional column conductor being
arranged such that the path of the at least one additional column
conductor crosses the path of the first row conductor. In another
embodiment, the at least one additional column conductor is a
plurality of additional column conductors, and each of the
plurality of additional column conductors are arranged such that
the path of each of the plurality of additional column conductors
crosses the path of the first row conductor. In another embodiment,
the at least one additional row conductor is arranged such that the
path of the at least one additional row conductor crosses the paths
of the first column conductor and the path of the at least one
additional column conductor.
The known-phase technique is compatible with, and may be
advantageous for use in connection with, certain touch sensor
technology, including but not limited to those various methods and
apparatus disclosed in the U.S. Patent Applications identified in
the first paragraph of this Detailed Description.
The present systems and methods are described above with reference
to block diagrams and operational illustrations of methods and
devices for frequency conversion and heterodyning. It is understood
that each block of the block diagrams or operational illustrations,
and combinations of blocks in the block diagrams or operational
illustrations, may be implemented by means of analog or digital
hardware and computer program instructions. These computer program
instructions may be provided to a processor of a general purpose
computer, special purpose computer, ASIC, or other programmable
data processing apparatus, such that the instructions, which
execute via the processor of the computer or other programmable
data processing apparatus, implements the functions/acts specified
in the block diagrams or operational block or blocks. In some
alternate implementations, the functions/acts noted in the blocks
may occur out of the order noted in the operational illustrations.
For example, two blocks shown in succession may in fact be executed
substantially concurrently or the blocks may sometimes be executed
in the reverse order, depending upon the functionality/acts
involved.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that various changes in form and
details may be made therein without departing from the spirit and
scope of the invention.
* * * * *